Screw spindle pump

ABSTRACT

The invention relates to a screw spindle pump ( 1 ) with a housing ( 2 ) which has an inlet ( 22 ) and an outlet ( 21 ) for a medium, with two spindles ( 3, 4 ) which are designed as shafts with respectively at least one external screw thread ( 31, 41 ), wherein the spindles ( 3, 4 ) are mounted next to each other in the housing ( 2 ) and the screw threads ( 31, 41 ) engage in each other in order to convey the medium from the inlet ( 22 ) to the outlet ( 21 ). The invention provides that each spindle ( 3, 4 ) is mounted in an axial bearing ( 5.1, 5.2 ) and the axial bearings ( 5.1, 5.2 ) are arranged diagonally opposite each other.

The invention relates to a screw spindle pump comprising a housing with an inlet and an outlet for a medium, comprising two spindles which are designed as shafts with at least one external screw thread, wherein the spindles are mounted next to each other in the housing such that the screw threads of the two spindles engage in each other in order to convey the medium from the inlet to the outlet.

Screw spindle pumps are displacement pumps in which two, three or more rotationally driven screw spindles convey a medium, in particular a fluid, within a volume enclosed by a housing from an inlet to an outlet of the housing. Screw spindle pumps differ inter alia in the number of screw spindles used, the thread pitch of the external screw thread, the mounting, the number of flows, and the torque transmission between the spindles.

In a two-spindle screw spindle pump, the medium is conveyed by two counter-rotating spindles with a left-hand and a right-hand screw thread. The thread flanks of the one spindle run in radial grooves between the thread flanks of the other spindle and vice versa. The medium is in this case conveyed in the axial direction in conveying chambers formed between the thread flanks of the screw thread.

As a result of the great radial forces acting on the spindles of a screw spindle pump, the spindles must be mounted in the radial direction. Most radial bearings can also absorb axial forces, which arise during conveyance of the medium, to a limited extent.

US 2009/0098003 A1 discloses a two-spindle and counter-flow screw spindle pump. The medium flows on the suction side via two inlet connectors into the housing and is conveyed by the two spindles from the outside inward to a central, pressure-side outlet connector. Both spindles of the screw spindle pump are mounted on their respective ends. The mounting in each case has sliding bearings and/or tilting-pad bearings in a combined axial/radial bearing housing.

Disadvantageous in the prior art is that axial force spikes in case of fluctuating or particularly high pressures cannot sufficiently be absorbed by radial bearings alone. When axial and radial bearings are combined, an uneconomic over-sizing of axial bearings results.

The task of the invention is to provide a screw spindle pump with an improved mounting of the spindles with regard to their operating behaviour and their economic viability.

The invention achieves the task posed by a screw spindle pump with the features of the principal claim. Advantageous embodiments and developments of the invention are disclosed in the subclaims, the description, and the figures.

The screw spindle pump with a housing which has an inlet and an outlet for a medium, with two spindles which are designed as shafts with at least one external screw thread each, wherein the spindles are mounted next to each other in the housing and the screw threads engage in each other in order to convey the medium from the inlet to the outlet, provides for each spindle to be mounted in an axial bearing and for the axial bearings to be arranged diagonally opposite each other.

As a result of the diagonal arrangement of the axial bearings, symmetric mounting in the axial direction is achieved. The occurring axial forces are absorbed uniformly by the axial bearings as a result so that axial mounting independent of the direction of rotation is achieved with minimum expenditures for bearings. A possible axial displacement of the two spindles is counteracted by the respective axial bearing. The risk of degradation of the efficiency of the screw spindle pump and damage to the screw spindle pump is reduced thereby.

The invention preferably relates to a screw spindle pump with precisely two axially parallel, counter-rotating spindles; four-spindle screw spindle pumps with a corresponding diagonal arrangement of the axial bearings can also be made.

The axial bearing is arranged on the spindle or is designed such that it prevents a displacement of the spindle in the axial direction. The axial bearing can be selected, arranged, and/or designed such that it can also absorb radial forces to a minor extent; alternatively, the axial bearing is designed such that it can substantially absorb only axial forces.

In a preferred embodiment of the invention, each spindle is mounted in precisely one axial bearing so that the screw spindle pump can be constructed with as small a number of components as possible. The axial bearings can be designed to act on both sides so that effective mounting is provided in both axial directions when the axial bearings are arranged diagonally on both spindles.

At least one axial bearing is preferably designed as a roller bearing. Particularly preferably, all axial bearings are designed as roller bearings, in particular as axial bearings acting on both sides. Roller bearings are bearings in which two components that can be moved relatively to each other are separated from each other by rolling bodies. The rolling bodies are arranged in a cage which holds the rolling bodies at a defined distance from each other. Balls and various roller types, such as cylinder rollers, tapered rollers, needle rollers, and barrel rollers can be used as rolling bodies. The use of roller bearings is advantageous in that the occurring friction is very low so that the wear of these bearings is also low. The use of roller bearings thus increases the economic viability of the screw spindle pump.

In one embodiment of the invention, at least one spindle is mounted in at least one additional radial bearing within the housing. Preferably, each spindle is mounted in two additional radial bearings within the housing, wherein the radial bearings of each spindle are arranged in the axial direction on both sides of the screw thread so that the screw threads are mounted between the two radial bearings. Accordingly, the two radial bearings of each spindle are opposite each other.

The suction-side and pressure-side radial bearings of the two spindles can be arranged in a combined radial bearing. The combined radial bearing can consist of a radial bearing insert with a number of individual bearing points or bearing bushings that corresponds to the number of spindles so that the spindles can be mounted in the bearing bushings. The bearing points of the radial bearing insert are advantageously constructed the same for the pressure side and the suction side so that symmetric mounting is provided. As a result, various radial bearing inserts do not have to be manufactured and kept in stock.

At least one radial bearing is advantageously designed as a roller bearing. Particularly preferably, all radial bearings are designed as roller bearings. Roller bearings are preferably suitable as radial bearings in the present invention because they allow axial movement of the spindles in addition to absorption of radial forces so that the axial forces are only absorbed by the axial bearings. As a result, the radial bearings are not additionally loaded by axial forces and the advantages of the diagonal arrangement of the axial bearings take effect.

In another advantageous embodiment of the invention, at least one axial bearing and/or at least one radial bearing is arranged in the delivery flow of the medium in order to be lubricated with the medium. All axial bearings and radial bearings can also be in the delivery flow. The axial bearings and radial bearings are preferably not sealed with respect to the medium but allow penetration of the medium. The medium-lubricated axial and/or radial bearings are preferably in the flow of the medium independently of the conveying direction, in particular a main delivery flow, not a bypass line or a forced bypass line. The axial and/or radial bearings are in this case lubricated with the medium independently of the conveying direction of the screw spindle pump. To this end, the bearings are designed to be accessible for the medium on both sides. In one embodiment of the invention, at least one lubrication groove and/or lubrication pocket is arranged in at least one of the radial bearings. Several lubrication pockets and/or lubrication grooves can be arranged uniformly over the periphery of the radial bearing in order to supply the bearing point uniformly with the lubricant. The lubrication groove and/or lubrication pocket is designed to receive the medium conveyed by the screw spindle pump. The lubrication pocket and/or lubrication groove preferably has an inlet and an outlet with is fluidically connected to the medium conveyed. This makes it possible to lubricate the bearing with the conveyed medium and to convey the medium to the bearing points during operation of the screw spindle pump. During a rotation of the spindles in the radial bearings provided with lubrication grooves and/or lubrication pockets, the medium conveyed is distributed in the bearing gap between the spindle and the radial bearing. Medium-lubricated internal mounting of the spindles is thereby possible; separate lubricants and a sealing of the bearing points are no longer required. The lubrication pockets and/or lubrication grooves have the advantage that they improve the lubrication of the radial bearings with the medium conveyed. The at least one lubrication groove is preferably formed in the axial direction of the radial bearing. This allows quick transport of the medium within the lubrication groove or lubrication pocket. The lubrication groove can extend over the entire length of the radial bearing so that the medium can enter and exit on the front sides and lubrication is ensured along the entire length of the radial bearing.

At least one axial bearing preferably abuts one radial bearing. All axial bearings can also abut against one radial bearing each. This is advantageous because a rotation of the rolling bodies in the axial bearing conveys the medium into and out of the axial bearing. This pumping action enhances the self-lubrication of the axial bearings and ensures in the case of abutting bearings, in particular in the case of bearings abutting directly against each other, that the axial bearing conveys the medium from the medium flow to the radial bearing and in particular to the bearing gap between the radial bearing and the spindle. If lubrication grooves or lubrication pockets are arranged with inlets between the axial bearing and the radial bearing, the conveyed medium is pushed into these inlets, whereby the lubricant throughput is increased and lubrication is improved.

The axial bearing is preferably arranged on the side of the radial bearing facing away from the screw thread in order to facilitate transport of the medium into the bearing gap of the radial bearing, in particular when the axial bearing is designed as a roller bearing. In other words, at least on one end section of at least one spindle, an axial bearing is arranged closer than a radial bearing on one end of the end section of the spindle. The arrangement of the radial bearings close to the screw threads, for example on a shaft shoulder or a shaft collar, ensures that bending of the spindles between two radial bearings each is minimised. The axial bearings are arranged further away from the at least one external screw thread. The end sections of the spindles are, for example, threadless sections of the spindles provided to be mounted in a bearing or to receive a bearing.

In another embodiment of the invention, the screw spindle pump has a direct drive for driving one of the spindles. In order to transmit the torque from the driven spindle to the non-driven spindle, a gearing mechanism which ensures a non-contact run of the screw threads can be provided.

The screw spindle pump is preferably single-flow. This means that the medium is only conveyed axially in one direction. In contrast to dual-flow screw spindle pumps, conveyance-related axial forces in single-flow screw spindle pumps cannot be compensated by a counter-flow arrangement; however, the direction of rotation in the single-flow screw spindle pump can be reversed without losses, whereby a greater flexibility in terms of installation and use can be achieved. The arrangement according to the invention of the axial bearings is therefore particularly advantageous in single-flow screw spindle pumps.

In this embodiment of the invention, the housing of the screw spindle pump has precisely one inlet and/or precisely one outlet for the medium. The inlet and/or outlet can be formed by at least one tube and/or at least one chamber, which tube or chamber can have a flange that allows the pump to be connected to a tube for transporting the medium.

In a variant of the invention, an inlet connector and/or outlet connector is oriented orthogonally to the longitudinal extent of the spindles, wherein the connectors are fluidically connected to a suction-side or pressure-side collecting chamber. The chamber can be arranged in the flow direction upstream or downstream of the spindles. The inlet connector can be oriented transversely to the axial orientation of the spindles.

In another embodiment of the invention, the conveying direction of the screw spindle pump can be reversed. The axial and/or radial bearings are preferably designed to be independent of the conveying direction and/or independent of the direction of rotation.

The diagonally opposite axial bearings and/or opposite radial bearings are preferably designed to be identical so that the same bearings, which must only be turned once to be used on the other side, are provided on both sides of the screw threads. The bearing arrangement preferably has a point symmetry. In a two-spindle screw spindle pump, the symmetry point is preferably a point in the centre between the screw threads.

An exemplary embodiment of the invention is explained below with reference to the drawings. They show:

FIG. 1 a longitudinal sectional view through an exemplary embodiment of a screw spindle pump according to the invention and

FIG. 2 a cross-sectional view through a spindle mounting according to FIG. 1.

FIG. 1 shows a longitudinal sectional view through an exemplary embodiment of a single-flow screw spindle pump 1 according to the invention. The screw spindle pump 1 has a housing 2, in which two axially parallel, counter-rotating spindles 3, 4 are mounted. The housing 2 has a suction-side inlet 22 and a pressure-side outlet 21. Both on the inlet 22 and on the outlet 21, a flange is respectively arranged on a connector, wherein FIG. 1 only shows the inlet connector with the inlet flange 22 b, via which the screw spindle pump 1 can be coupled to upstream devices or suction lines. The outlet connector in the embodiment shown is above the sectional plane; the pump can be connected to downstream devices via an outlet flange. The inlet 22 for the medium entering the screw spindle pump 1 has an inlet chamber 22 a, which is arranged upstream of the spindles 3, 4 in the axial direction of said spindles. The outlet 21 of the housing 2 for the medium exiting the screw spindle pump 1 has an outlet chamber 21 a, from which branches off a connector or an outlet flange, through which the conveyed medium can then exit. On the suction side, the inlet chamber 22 a enlarges from the flange 22 b toward the spindles 3, 4. The structure of the screw spindle pump 1 can however also be reversed and can have the inlet on the side of the outlet and the outlet on the side of the inlet of the embodiment shown with an outlet chamber tapering toward the outlet flange.

The screw spindle pump 1 has a first, driven spindle 3, whose one spindle end 32 is guided through a sealed opening in the housing 2. On this spindle end 32, a drive not shown, e.g., a direct drive, can be arranged in order to drive the first spindle 3. Via a gearing mechanism not shown, e.g., two gear wheels with the same number of teeth, the torque of the driven first spindle 3 can be transmitted to the second spindle 4. Both spindles 3, 4 have external screw threads 31, 41, have the same pitch, and mesh with each other so that the medium is conveyed from the inlet 22 to the outlet 21 during rotation of the spindles 3, 4. It is in principle also possible for the second spindle 4 to be driven via the screw threads 31, 41.

The spindles 3, 4 are mounted on their inlet-side end sections in radial bearings 6.1, 6.2 within the housing 2. On the outlet side, the driven first spindle 3 is mounted on a shaft shoulder in a radial bearing 6.2 and an additional axial bearing 5.2. The shaft shoulder is adjoined by the shaft section which comprises the spindle end 32 and is guided out of the housing 2. On its outlet-side shaft end, the second spindle 4 is only mounted in the radial bearing 6.1. The radial bearings 6.1, 6.2 are designed as sliding bearings in the exemplary embodiment. On the inlet side, an axial bearing 5.1 is additionally arranged on the second spindle 4 in order to transfer occurring axial forces via an axial bearing seat 8.1 into the housing 2. Correspondingly, a second axial bearing 5.2 is mounted on the outlet side in another axial bearing seat 8.2 in order to support the first spindle 3. Axial forces that arise during operation of the screw spindle pump 1 and act on the spindles 3, 4 are transferred via the two diagonally arranged axial bearings 5.1, 5.2 via the respective axial bearing seats 8.1, 8.2 into the housing 2. Both the axial bearings 5.1, 5.2 designed as roller bearings and the radial bearings 6.1, 6.2 designed as sliding bearings are arranged in the flow of the medium. To each spindle 3, 4 is assigned only precisely one axial bearing 5.1, 5.2; the axial bearings 5.1, 5.2 can be designed to be acting on both sides and are fixed via a shaft collar and a shaft nut on the respective spindle 3, 4.

Both spindles 3, 4 are respectively mounted in a combined radial bearing 6.1 and 6.2, which are fixed in the housing 2. The combined radial bearings 6.1, 6.2 are sliding bearings with a common bearing body 6 for both spindles 3, 4; the bearing points in the exemplary embodiment are formed in the bearing body 6; alternatively, bearing bushings can be inserted into the bearing body 6. The combined radial bearings 6.1 and 6.2 are arranged in the flow of the medium. The two axial bearings 5.1, 5.2 abut against the respective radial bearing 6.1, 6.2 on the outside. The medium conveyed is guided from the inlet 22 through the chamber 22 a to the first inlet-side axial bearing 5.1 and the inlet-side radial bearing 6.1. Through the first axial bearing 5.1, the conveyed medium is guided to the bearing point of the second spindle 4 in the radial bearing 6.2; the inlet-side radial bearing 6.1 of the first spindle 3 is located directly in the medium flow. The design of the first axial bearing 5.1 as roller bearing enhances the inflow of the conveyed medium as a result of the direct adjacency of the two bearings and as a result of the pump effect through the roller bearing body in the axial bearing 5.1. The housing 2 respectively forms a free space 9 between the bearing body 6 of the radial bearings 6.1, 6.2 and the screw threads 31, 41. The shaft diameters of the spindles 3, 4 are smaller in this free space 9 than in the bearing body 6. Conveyed medium moreover passes through recesses in the housing 2 from the inlet chamber 22 a into the free space 9 with the shaft shoulders 32, 42 and is guided by the rotation of the screw threads 31, 41 to the outlet-side free space 9 and thus to the bearing points of the outlet-side radial bearings 6.1, 6.2. With the front sides facing the screw threads 31, 41, the outlet-side radial bearings 6.1, 6.2 are also located directly in the conveyed medium flow; the outlet-side axial bearing 5.2 is located in the flow direction downstream of the radial bearing 6.2. On the front side of the radial bearings 6.1, 6.2 are formed inlets 72 and outlets 71 for lubrication grooves or lubrication pockets, the function and structure of which are explained below.

FIG. 2 shows a sectional view through the combined radial bearing 6.1, 6.2 and the housing 2 of the screw spindle pump 1 of FIG. 1 with a view toward the axial bearing 5.2. The radial bearing consists of a bearing body 6 with two bores 63, 64 for forming the bearing points for the shaft end of the second spindle 4 and the shaft shoulder of the first spindle 3. The bearing body 6 is inserted into the housing 2 and fixed there. In the housing 2, recesses 25 surrounding the bearing body 6 are formed. On the inlet side, the medium to be conveyed enters the inlet chamber 22 a through the inlet 22 and is transported to the bearings 6.1, 6.2, 5.1. Through the bearings and in particular through the free spaces 25, the medium is transported through the free space 9 to the screw threads 31, 41 and through them to the outlet-side free space 9. On the outlet side, the conveyed medium under pressure passes from the free space 9 between the screw threads 31, 41 and the outlet-side radial bearings 6.1, 6.2 through the recesses 25, and a minor portion thereof through the bearings 6.1, 6.2, 5.2, into the outlet chamber 21 a and from there exits the pump.

Two lubrication grooves 7 are respectively formed in two bores 63, 64 of the bearing body 6. The grooves 7 extend in the axial direction and open on the front sides of the bearing body 6 so that conveyed medium can be used as lubricant independently of the conveying direction and direction of rotation of the pump. More than two lubrication grooves 7, which are preferably uniformly distributed over the periphery of the bores 63, 64, can also be formed in the bores 63, 64 or, where applicable, in the bearing bushings. The grooves 7 have a substantially semi-circular cross-section. As described above, the conveyed medium can enter the lubrication grooves 7 through the front-side inlets 72 in order to uniformly distribute the medium between the spindles 3, 4 and the bearing points of the combined radial bearing 6.2 so that sufficient and uniform lubrication is brought about.

The grooves can also have a different cross-sectional shape. Lubrication pockets that are fluidically connected to the delivery flow, i.e., are provided with an inlet and an outlet, can also be formed in the bores.

With only two axial bearings 5.1, 5.2, the described embodiment of the screw spindle pump 1 allows a construction of the mounting that is independent of the direction of rotation and thus independent of the conveying direction. All bearings are located in the main delivery flow and are completely lubricated with medium. The bearing bodies 6 are exchangeably mounted in the housing 2 so that they can be easily exchanged if they must be replaced as a result of wear or adapted to another embodiment with different spindles 3, 4. The bearing bodies 6 are attached to the recesses 25 in one housing wall 26 so that the entire flow of the conveyed medium impinges on the front sides of the radial and axial bearings 5.1, 5.2, 6.1, 6.2 and makes lubrication with medium possible. The diagonal arrangement of the axial bearings 5.1, 5.2 with a bearing on the pressure side of the spindle 3 and a bearing on the suction side of the second spindle 4, each on the sides of the radial bearings 6.1, 6.2 facing away from the screw threads 31, 42, ensures a bearing construction of the same type on both bearing sides with bearing and lubrication properties that are independent of the direction of rotation and thus of the conveying direction. In an embodiment of the axial bearings 5.1, 5.2 as roller bearings, the pump effect generated by the rolling bodies is utilized to improve lubrication of the radial sliding bearings 6.1, 6.2. The mounting is designed to be point-symmetric so that a corresponding force distribution in the mounting is maintained even if the direction of rotation of the spindles is reversed. The respective inlet of the one conveying direction then becomes the outlet in the reverse conveying direction and vice versa.

LIST OF REFERENCE SYMBOLS

-   1 screw spindle pump -   2 housing -   21 outlet -   21 a outlet chamber -   22 inlet -   22 a inlet chamber -   22 b flange -   26 housing wall -   3, 4 spindles -   31, 41 screw thread -   5.1, 5.2 axial bearing -   6 bearing body -   6.1, 6.2 radial bearing -   63 bore -   64 bore -   7 lubrication groove -   71 outlet -   72 inlet -   8.1 axial bearing seat -   8.2 axial bearing seat -   9 free space 

1. A screw spindle pump with a housing which has an inlet and an outlet for a medium, with two spindles which are designed as shafts with at least one external screw thread each, wherein the spindles are mounted next to each other in the housing and the screw threads engage in each other in order to convey the medium from the inlet to the outlet, wherein each spindle is mounted in an axial bearing and the axial bearings are arranged diagonally opposite each other.
 2. The screw spindle pump according to claim 1, wherein each spindle is mounted in precisely one axial bearing.
 3. The screw spindle pump according to claim 1, wherein at least one axial bearing is designed as a roller bearing.
 4. The screw spindle pump according to claim 1, wherein at least one spindle (3, 4) is mounted in at least one additional radial bearing (6.1, 6.2) in the housing (2).
 5. The screw spindle pump according to claim 4, wherein each spindle is mounted in the housing on both sides of the screw thread in two radial bearings.
 6. The screw spindle pump according to claim 4, characterised in that at least one radial bearing (6.1, 6.2) is designed as a sliding bearing.
 7. The screw spindle pump according to claim 4, wherein the at least one axial bearing and/or the at least one radial bearing is arranged in a flow of the medium.
 8. The screw spindle pump according to claim 4, wherein at least one lubrication pocket and/or one lubrication groove is arranged in at least one of the radial bearings.
 9. The screw spindle pump according to claim 8, wherein the lubrication pocket and/or lubrication groove has an inlet and an outlet which is fluidically connected to the medium conveyed.
 10. The screw spindle pump according to claim 4, wherein the axial bearing abuts against one of the radial bearings.
 11. The screw spindle pump according to claim 4, wherein the axial bearing is arranged on the side of the radial bearing facing away from the screw thread.
 12. The screw spindle pump according to claim 1, wherein the screw spindle pump has a direct drive for driving one of the spindles.
 13. The screw spindle pump according to claim 1, wherein the screw spindle pump is single-flow. 